Soap Bubble

Classical Mechanics Level 2

Air is pushed into a soap bubble of radius $r$ to double its radius. If the surface tension of the soap solution is $S$ , the work done in the process is:

16\pi r^{2}S

12\pi r^{2}S

24\pi r^{2}S

8\pi r^{2}S

1 solution

A Former Brilliant Member
Feb 4, 2018

$\text{Increase in surface area} = ds = 2 \times 4\pi \times ((2r)^{2} - (r)^{2}) = 24\pi r^{2}$

$\text{Work done} = ds \times S = 24\pi r^{2}S$

$\text{A soap bubble has 2 surface layers, making 4 forces come into the picture. Hence, we multiply 2 with the usual surface area of a sphere.}$

By two surface layers do you mean both the inner sphere and the outer sphere surfaces?

Akhash Raja Raam - 3 years, 4 months ago

Soap bubble has a thickness, so outer - thickness and thickness - inner.

A Former Brilliant Member - 3 years, 4 months ago

Seems like I was right. Thanks!

Akhash Raja Raam - 3 years, 4 months ago

@Akhash Raja Raam – But it seems you did not tick the correct answer, so how were you right in the first place.......

A Former Brilliant Member - 3 years, 4 months ago

@A Former Brilliant Member – Yeah. I didn't tick the correct answer but then I had an idea that I made a mistake in not taking both the surfaces into account. Your answer and clarification told me that I was right in guessing where I was wrong! :)

Akhash Raja Raam - 3 years, 4 months ago

@Akhash Raja Raam – Good. Keep it up.

A Former Brilliant Member - 3 years, 4 months ago

@A Former Brilliant Member – Sure, thanks!

Akhash Raja Raam - 3 years, 3 months ago

Soap Bubble

1 solution

0 pending reports